The present invention relates to a process for preparing particles of a high water-absorbent resin, and more particularly to a process for preparing particles of a high water-absorbent resin which is suitably utilizable for sanitary goods such paper diapers, sanitary napkins, tampons and disposable dustclothes, water-retaining agents or soil conditioners in the fields of agriculture and horticulture, and other various uses of coagulation of sludge, prevention of dew condensation on building materials, dehydration of oil, and so on.
Water-absorbent resins have, hitherto, been used in the manufacture of paper diapers, sanitary napkins, tampons, disposable dustcloths and other sanitary goods, and as water-retaining agents or soil conditioners in the fields of agriculture and horticulture. They have been also used for the purpose of coagulation of sludge, prevention of dew condensation on building materials, dehydration of oil, and so on.
These known water-absorbent resins include crosslinked polyacrylic acid salts, hydrolyzates of crosslinked acrylic acid ester-vinyl acetate copolymers, crosslinked starch-acrylic acid salt graft copolymer, hydrolyzates of crosslinked starch-acrylonitrile graft copolymers, crosslinked polyvinyl alcohol grafted with maleic anhydride, crosslinked polyethylene oxide, and so on.
These high water-absorbent resin powders are prepared in a manner wherein a high water-absorbent polymer is prepared in reversed phase suspension polymerization, reversed phase emulsion polymerization, aqueous solution polymerization or a polymerization using an organic solvent, then the prepared polymer is dried as it is, further, when occasion demands, the dried one is pulverized.
The high water-absorbent resin powders prepared by the above-mentioned manners, however, are wide in particle size distribution and have quite a number of fine particles. When using the high water-absorbent resin particles in manufacture of the sanitary goods, in general, the particles are admixed with a pulverized pulp, are uniformly placed on the pulverized pulp layer, or are put between water-absorbing papers. Accordingly, if using the water-absorbent resin particles having quite a number of fine particles, not only it is troublesome to handle them, for instance, the bridging is easily caused during transportion or supply of the particles, but also the working surrounding is made remarkably bad or there is a case that the pollution or trouble of the apparatus is caused due to the dust. Further, the fine particles are got out of the surface or outer border of the sanitary good through the spaces between the pulp fibers.
As a process for preparing particles of a water-absorbent resin which improves the above-mentioned defects, there are processes described in Japanese Unexamined Patent Publication No. 61-97333 and No. 61-101536, wherein a mixture of a high water-absorbent resin powder and an inorganic powder is stirred by using a specific apparatus, and on the mixture is spraied an aqueous liquid such as water alone, an aqueous mixture of water and an organic solvent compatible with water, or an aqueous solution wherein a water-soluble hight molecular weight compound is dissolved in water or the aqueous mixture as mentioned above. The processes have, however, a defect that if a condition that the mixture is stirred at high speed by using a specific appatratus, on which the aqueous liquid is spraied in the sate of a fine droplet is not satisfactory, the blocking of the resin particles is caused partially.
Also, Japanese Unexamined Patent Publication No. 62-132936 discusses a process wherein an inorganic powder is added to a mixture of a high water-absorbent resin, water and a surfactant having an HLB (hydrophile-lypophile balance) of 6 to 12 in an inert solvent. However, according to the process, not only the use of the inert solvent is disadvantageous from the viewpoint of the recovery thereof but also since the solvent easily remains in the final particles, the particles are not sanitary. Moreover since the solvent easily catches fire, the particles are defective in safety.
It is an object of the present invention is to provide a process for preparing particles of a high water-absorbent resin which improves the above-mentioned defects.
This and other objects of the present invention will become apparent from the description hereinafter.